In recent years, together with the reviewing of energy policies, strong promotions have been made to spread supply infrastructure of hydrogen stations for fuel cell vehicles. In piping facilities in which high-pressure fluid flows such as a hydrogen station, for example, in a case of hydrogen, hydrogen reaches a high pressure of 80 MPa or more. Therefore, a valve for high-pressure fluid is used. As a valve for flowing such a high-pressure fluid, for example a needle valve disclosed in Patent Document 1 is known. The needle valve has a structure in which a flow channel opens and closes by reciprocation movement of a needle.
Meanwhile, a trunnion ball valve may be used as a valve suitable for a case in which a flow channel is switched on or off while maintaining its flow. A known ball valve of this type is, for example, a trunnion ball valve of Patent Document 2. This trunnion ball valve is structured so that a ball made of metal is provided inside a body in a rotatable manner via a stem and a trunnion (lower stem), and a seat retainer is provided in which a ball seat for sealing is provided on both sides of the ball. Such a valve for high pressure requires maintaining high sealing performance to securely prevent leakage. Furthermore, in order to secure operability of the valve under high pressure, it is also necessary to satisfy sliding ability between the stem and the seat.
One example of a trunnion ball valve for high pressure gas for improving sealing performance between the ball and the seat is a ball valve disclosed in Patent Document 3. In order to improve the sealing performance between the ball and the seat under high pressure, this ball valve has diamond-like carbon deposited on the ball on a surface with which the seat is in contact.
Moreover, Patent Document 4 discloses a solenoid valve as a valve on which a film formed by diamond-like carbon is provided. The solenoid valve has a coating film formed on at least one sliding surface of an inner surface of a valve casing or an outer surface of a ball. Diamond-like carbon is used as the coating film, to improve the sliding ability.